1. Field of the Invention
The present invention relates to hermetically sealed glass packages suitable to protect thin film devices which are sensitive to the ambient environment, and more particularly to a method of sealing such devices
2. Technical Background
OLEDs have been the subject of considerable research in recent years because of their use and potential use in a wide variety of electroluminescent devices. For instance, a single OLED can be used in a discrete light emitting device or an array of OLEDs can be used in lighting or flat-panel display applications (e.g., OLED displays). OLED flat panel displays in particular are known to be very bright and to have good color contrast and wide viewing angle. It is well known that the life of the OLED display can be significantly increased if the electrodes and organic layers located therein are hermetically sealed from the ambient environment. However, OLED displays, and in particular the electrodes and organic layers located therein, are susceptible to degradation resulting from interaction with oxygen and moisture leaking into the OLED display from the ambient environment. Unfortunately, in the past it has been very difficult to develop a sealing process to hermetically seal the OLED display. Some of the factors that made it difficult to properly seal the OLED display are briefly mentioned below:                The hermetic seal should provide a barrier for oxygen (10−3 cc/m2/day) and water (10−6 g/m2/day).        The size of the hermetic seal should be minimal (e.g., <2 mm) so it does not have an adverse effect on size of the OLED display.        The temperature generated during the sealing process should not damage the materials (e.g., electrodes and organic layers) within the OLED display. For instance, the first pixels of OLEDs which are located about 1-2 mm from the seal in the OLED display should not be heated to more than 100° C. during the sealing process.        The gases released during sealing process should not contaminate the materials within the OLED display.        The hermetic seal should enable electrical connections (e.g., thin-film chromium electrodes) to enter the OLED display.        
One way to seal the OLED display is to form a hermetic seal by melting a low temperature frit doped with a material that is highly absorbent at a specific wavelength of light. For example, a high power laser may be used to heat and soften the frit which forms a hermetic seal between a cover glass with the frit located thereon and a substrate glass with OLEDs located thereon. The frit is typically ˜1 mm wide and ˜6-100 um thick. If the absorption and thickness of the frit is uniform then sealing can be done at a constant laser energy and translation speed so as to provide a uniform temperature rise at the frit location. However, when the frit is relatively thin, 100% of the laser energy is not absorbed by the frit. For example, some of the laser energy can be absorbed or reflected by metal electrodes that are attached to the OLEDs on the substrate glass. Since it is desirable to use thin frits, and the metal electrodes have different reflectivity and absorption properties as well as different thermal conductivities from the bare substrate glass, this situation can create an uneven temperature distribution within the frit during the sealing process which subsequently can lead to a non-hermetic connection between the cover glass and the substrate glass. In addition, high absorption by the electrodes may result in overheating of, and subsequent damage to, the electrodes. This sealing problem is solved by using one or more of the sealing techniques of the present invention.